The present invention relates to a method and an apparatus for transfer of preformed hollow sections which are to be welded.
Methods and apparatus for the fabrication of welded tubes or other hollow sections have long been known to the expert. Fundamentally in all these methods or apparatus a flat metal sheet is shaped into a section with the desired profile by means of a forming machine. This may involve drawing the flat sheet from a coil and shaping it into a straight-sided or round hollow section by means of a continuous forming process. In other forming machines the flat sheet is drawn from a stack and is shaped into the desired profile step-by-step by means of forming tools. The hollow sections thus preformed are then fed to a welding machine for welding of the butt joint formed by the edges of the sheet.
In the fabrication of hollow sections suitable for use in motor vehicle bodies, the welded sections are subjected to a further forming process. For this forming process, the hydroforming technique is nowadays increasingly employed. This forming technique makes it possible to bend and/or bulge-form given sections as desired, but it imposes more demanding requirements on the quality of the welded joint.
Welding machines that are capable of meeting these more demanding quality-requirements are likewise known to the expert. These machines feature (inter alia) special devices for stabilizing the joint in the preformed parts and feeding it to the laser welding beam with the necessary precision.
In these precision high-power laser welding machines, transfer of the preformed hollow sections is manual. Firstly, this makes it possible to accommodate to the different processing rates of the individual forming machine and the welding machine used. Secondly, the precision welding machine is decoupled from the vibrations produced by the forming tools.
DE-U 8713471 discloses a welding machine for tubes in which a feeler roller engages in the joint between the edges to be welded in order to track the position of the laser beam. EP-A 0672496 discloses a laser processing plant for laser welding flanges to tubes and for cutting openings in the tube walls. U.S. Pat. No. 2,607,310 discloses a workpiece holder for arc welding of tubes.
A problem that can be addressed by the present invention, therefore, is to provide a mechanized transfer of preformed hollow-section blanks between hollow-section machine-tools and precision welding machines that allows preformed parts to be fed into a precision high-power laser welding machine in a time-optimized and vibration-free manner and with the necessary accuracy, so that they can be welded to yield hollow sections suitable for further forming into motor vehicle body components.
This problem is solved by a method in which the blank is seized by a transfer apparatus adapted to remove it from the forming tool and feed it to the welding machine, and is adjusted thereby so that the joint of the blank is in line with the welding point of the welding machine.
In a further process step the edges to be joined are positioned as desired and are presented together at least in the region of the welding point.
An apparatus according to the invention can include an apparatus which has means for seizing the preformed hollow-section blank that are adapted to remove the blank from the forming tool and feed it to the welding machine. By the same means, the joint of the blank can be adjusted so that it is in line with the welding point of the welding machine. Additional means are provided for positioning the joint edges as desired and for pressing the positioned joint edges together at least in the region of the welding point.
Particular embodiments are defined by the features of the dependent claims.
Developments of this method and of this apparatus lie within the skill of the expert, and fall especially into the category of additional measures for monitoring the welding process and controlling the quality of the welded seam. It will be evident that the welding machine can also be provided with a welding beam that is traversable along the joint, and that a weld seam cleaning operation following after the welding operation can be provided. For this transfer method according to the invention and its transfer apparatus, it is of course possible to use welding machines that are not subject to any special requirements as regards precision.